Preheat the oven to 350 degrees Fahrenheit. In a large bowl, stir together the flour, sugar, salt and baking powder until well blended. Add the butter and beat with an electric mixer until the mixture looks grainy. Add the milk and vanilla extract and mix together at medium speed for one minute. Add one egg at a time, beating at medium high speed for 30 seconds after each addition.

Once you have added all of the eggs, add the food coloring and blend until the mixture is the same color throughout. Then gently stir in the grated Symphony bar using a wooden spoon. Pour the cake mixture evenly into two well-greased 9-inch circular cake pans. Bake for 25-35 minutes, or until a knife or toothpick inserted into the middle of each cake layer comes out clean. Allow the cake to cool for 15 minutes after removing it from the oven.

Shake the pan a little bit to loosen the grip of the cake, then place a plate on top of the pan and, wearing oven mitts, flip it over so that the pan is on the top and the plate is on the bottom. Gently remove the pan and place the plated cake layer in the refrigerator for 30 minutes. Repeat this process with the second cake pan as well. While the cake is cooling, begin making the dark chocolate frosting. Then place the bottom cake layer onto the display surface, (i.e. a cake stand or serving plate), and begin evenly frosting the top of the bottom cake layer. Then, center the second cake layer on top of the bottom cake layer so that they line up perfectly. Now frost the sides and top of the cake so that the entire cake surface is frosted and no cake surface is visible through the frosting. Serve at room temperature.